Easy-open container and closure assembly therefor

ABSTRACT

A container comprises a container body defining a top opening, a sealing surface being defined on the container body encircling the top opening, and a closure sealed to the sealing surface by a heat-seal material comprising a blend of two different acidic ionomers having respectively higher and lower acid content such that the heat-seal material has an acid content intermediate between that of the two different ionomers, whereby the resulting heat seal strikes a balance between oil-resistance and age-up.

BACKGROUND OF THE INVENTION

1. Technical Field

The invention relates generally to easy-open containers for consumerproducts, wherein the container is sealed closed by heat-sealing aflexible membrane closure to a metal end, flange, or rim that encirclesthe top opening of the container. The invention more particularlyrelates to such a container employing a heat-seal material composed ofan acidic ionomer.

2. Description of Related Art

There is a class of easy-open product containers that are sealed closedby heat-sealing a membrane closure to a metal end or to a flange or rimthat encircles the open top of the container. Such containers, forexample, are marketed under the ULTRASEAL® trademark for containingvarious food products. In the case of containers having a metal end, themetal end generally comprises tin-plate steel, and its upper surface iscoated with a heat-seal material The metal end is double-seamed to aflange formed on the container. The membrane closure can have variousconstructions, often including a foil layer as a barrier, and/or one ormore polymer layers. The lower surface of the membrane closure has aheat-seal material on it for heat-sealing to the heat-seal materialcoated on the metal end.

In prior seals of this type, the heat-seal material that has been usedis an acidic ionomer, in particular an ethylene methacrylic acid ionomer(i.e., a copolymer of ethylene and methacrylic acid wherein themethacrylic acid groups are partially neutralized with a cation,typically zinc or sodium ions), such as the composition marketed underthe SURLYN® trademark by DuPont. Current ionomer heat-seal material usedin this sealing application has an acid content of about 15%. Thisrelatively high acid content provides grease-resistance to the bondbetween the membrane closure and the metal end. However, the bond tendsto become stronger with aging, to the point that it can become verydifficult for the consumer to remove the membrane closure from the metalend.

BRIEF SUMMARY OF THE INVENTION

It has been discovered that a higher acid content of the heat-sealmaterial promotes such bond-strengthening with age (referred to as the“age-up” phenomenon). The invention addresses this problem by providinga heat-seal material comprising a blend of two different acidic ionomersof respectively higher and lower acid content such that the resultingblend has an intermediate acid content. In one embodiment, themore-acidic ionomer has an acid content of about 15% and the less-acidicionomer has an acid content of about 7%, and the blend containsapproximately equal proportions of the two ionomers, such that the acidcontent of the blend is about 11%. The reduced acid content of theresulting blend leads to a reduction in the age-up problem, while stillretaining sufficient oil- and grease-resistance for the seal.

In a preferred embodiment, the more-acidic ionomer comprises an ethylenemethacrylic acid ionomer (i.e., a copolymer of ethylene and methacrylicacid wherein the methacrylic acid groups are partially neutralized witha cation, typically zinc or sodium ions), such as the compositionmarketed under the SURLYN® trademark by DuPont. The less-acidic ionomercomprises an ethylene acrylic acid ionomer (i.e., a copolymer ofethylene and acrylic acid wherein the acrylic acid groups are partiallyneutralized with a cation, typically zinc or sodium ions), such as thecomposition marketed under the TRANCEND® trademark by DuPont.

A container in accordance with one embodiment of the invention comprisesa container body defining a top opening, a sealing surface being definedon the container body encircling the top opening, and a closure sealedto the sealing surface by a heat-seal material comprising a blend of twodifferent acidic ionomers having respectively higher and lower acidcontent such that the heat-seal material has an acid contentintermediate between that of the two different ionomers, whereby theresulting heat seal strikes a balance between oil-resistance and age-up.

A container in accordance with another embodiment of the inventioncomprises a container body defining a top opening, a metal end attachedto the container body encircling the top opening, and a membrane closuresealed to the metal end by a heat-seal material comprising a blend oftwo different acidic ionomers having respectively higher and lower acidcontent such that the heat-seal material has an acid contentintermediate between that of the two different ionomers.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Having thus described the invention in general terms, reference will nowbe made to the accompanying drawings, which are not necessarily drawn toscale, and wherein:

FIG. 1 is a perspective view of a container in accordance with oneembodiment of the invention;

FIG. 2 is a cross-sectional view of a metal end and membrane closure fora container such as shown in FIG. 1;

FIG. 3 is an enlarged, exploded fragmentary view of the metal end andmembrane closure in the vicinity of the heat seal therebetween; and

FIG. 4 is a fragmentary cross-sectional view through the container takenalong line 4-4 in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The present inventions now will be described more fully hereinafter withreference to the accompanying drawings, in which some, but not allembodiments of the invention are shown. Indeed, these inventions may beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will satisfy applicable legalrequirements. Like numbers refer to like elements throughout.

A container 10 in accordance with one embodiment of the invention isdepicted in FIGS. 1-4. The container includes a container body 100 thatcan have various constructions. Typically the container will include agenerally tubular or conical side wall 12 whose upper end defines a topopening of the container. The side wall 12 can be formed of variousmaterials, including but not limited to plastic (e.g., the containerbody can be thermoformed or blow-molded from polymer material(s)) orcomposite (e.g., the side wall can be formed of paperboard laminatedwith an impervious liner of various constructions). The container bodyincludes a flange 101 (FIG. 4) that projects generally radiallyoutwardly from the upper edge of the side wall 12.

An end member 20 is attached to the container body 100 by double-seamingwith the flange 101. With reference to FIG. 2 in particular, the endmember 20 is a generally ring-shaped structure. The radially outer edgeportion of the end member 20 has a curl 21 that defines a generallyannular channel for receiving the flange 101 on the container body. Theend member 20 is formed of a material that renders it plasticallydeformable. The curl 21 on the end member, along with the flange 101, isdeformed or rolled under using conventional double-seaming equipment toform a hermetic double seam as shown in FIG. 4. The end member includesa radially inner portion or ledge 23 that extends radially inwardly fromthe double seam and defines a central opening 24 through which access tothe interior of the container can be had. The radially inner edge of theend member can be rolled (not shown), if desired, such as shown in U.S.Pat. No. 5,752,614, which is incorporated herein by reference.

The end member 20 can be formed of various materials, as long as it isplastically deformable so as to accommodate the double-seamingoperation. For example, the end member can be formed of a suitable metalsuch as aluminum or tin-plate steel of relatively large thickness, e.g.,about 0.005 to about 0.025 inch. Metal end members on food containerstypically are coated with a suitable coating (not shown) to preventdirect contact between the metal and the container contents. Analternative end member material is composite material comprising arelatively thin metal foil of aluminum or steel laminated with one ormore polymer layers, such as disclosed in U.S. Pat. No. 5,069,335,incorporated herein by reference. The metal foil layer in such acomposite end member is substantially thinner than a conventional metalend member, e.g., about 0.00015 to 0.003 inch for aluminum and about0.0005 to 0.0025 inch for steel. The particular construction of the endmember is not critical to the present invention, and various otherconstructions can be used.

The container 10 also includes a flexible membrane closure 30 that isattached to the end member 20 by heat-sealing, in such a manner that theclosure is readily peelable from the end member to open the container.The closure preferably includes a tab portion 33 that remains unattachedto the end member after heat-sealing (see FIG. 2) and is positioned tobe grasped and pulled to open the container. The membrane closure can beformed of various materials or combinations of different materials. Theclosure includes at least one structural layer of suitable materialhaving adequate strength properties to support the forces expected to beexerted on the closure during packaging, subsequent processing (e.g.,retort), and shipping and handling. Where barrier performance againstoxygen and/or moisture or other substances is needed, the closure alsoincludes at least one barrier layer (which can also be a structurallayer, or can be separate from the structural layer). For instance, theclosure can comprise a metal foil layer (which provides both structuralproperties as well as barrier performance), in which case the undersideof the foil typically will have a coating of a suitable material toprevent direct contact between the container contents and the metal;such coating may constitute a heat-seal material, or may be separate anddistinct from the heat-seal material provided on the closure forheat-sealing the closure to the end member. Other membrane closureconstructions are possible, such as polymer film (or multiple polymerfilm layers laminated or coextruded together) with or without otherlayers such as metal foil or paper. The particular construction of themembrane closure is not critical to the present invention.

To attach the membrane closure 30 to the end member 20, each of thesecomponents has a heat-seal material disposed thereon. As shown in FIG.3, the closure includes a heat-seal material 31 disposed on at leastthat portion of the closure that contacts the end member 20. Theheat-seal material can be provided on the closure in various ways. Forexample, the heat-seal material can be extrusion-coated onto theclosure; alternatively, a heat-seal material web can be formedseparately from the closure and then laminated to the closure inconventional fashion; as still another alternative, in the case of anall-polymer closure, the heat-seal material and the other layer(s) ofthe closure can be coextruded simultaneously.

The end member 20 likewise has a heat-seal material 25 disposed on atleast the ledge portion 23 that is contacted by the closure 30 (i.e.,disposed on at least the sealing surface to which the closure is to beattached); the heat-seal material 25 can, if desired, cover the entireupper surface of the end member. There may be one or more interveninglayers (not shown), such as adhesive layers, between the heat-sealmaterial 25 and the main substrate of the end member to facilitateadhering the heat-seal material to the substrate and/or for otherpurposes. The presence or absence of such additional layer(s) is notcritical to the present invention.

In accordance with the invention, the heat-seal material 25, 31comprises a blend of two different acidic ionomers having differentlevels of acid content. More particularly, the heat-seal material in apreferred embodiment comprises a blend of a first ionomer having an acidcontent of about 15% by weight, and a second ionomer having an acidcontent of about 7% by weight. The first and second ionomers are presentin approximately equal proportions in the preferred embodiment.Preferably, the first ionomer comprises an ethylene methacrylic acidionomer (i.e., a copolymer of ethylene and methacrylic acid wherein themethacrylic acid groups are partially neutralized with a cation,typically zinc or sodium ions), such as the composition marketed underthe SURLYN® trademark by DuPont. The second ionomer preferably comprisesan ethylene acrylic acid ionomer (i.e., a copolymer of ethylene andacrylic acid wherein the acrylic acid groups are partially neutralizedwith a cation, typically zinc or sodium ions), such as the compositionmarketed under the TRANCEND® trademark by DuPont. When equal proportionsof these two ionomers are blended, the resulting heat-seal material hasan acid content of about 11% by weight.

The reduced acid content of the heat-seal material (i.e., reducedrelative to the conventional SURLYN® material that has typically beenused in the past, which has a 15% acid content) has been found to leadto a reduction in the age-up phenomenon. At the same time, heat sealsproduced using the material still have adequate oil- andgrease-resistance.

Many modifications and other embodiments of the inventions set forthherein will come to mind to one skilled in the art to which theseinventions pertain having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. For example,although the sealing surface to which the closure 30 is heat-sealed inthe disclosed embodiment is defined on a ring-shaped end member 20 thatis double-seamed to the container body, it is within the scope of theinvention to provide the sealing surface in other ways, such as byintegrally forming the sealing surface on the container body.Additionally, while the sealing surface is shown as being planar andnormal to a longitudinal axis of the container body, alternatively thesealing surface could be shaped and/or oriented in other ways. It willalso be appreciated that although a container of circular cross-sectionhas been described, the invention is not limited to circular containers;terms such as “ring-shaped”, “encircling”, and the like, as used in thespecification and claims, are intended to apply to both circular andnon-circular objects. Therefore, it is to be understood that theinventions are not to be limited to the specific embodiments disclosedand that modifications and other embodiments are intended to be includedwithin the scope of the appended claims. Although specific terms areemployed herein, they are used in a generic and descriptive sense onlyand not for purposes of limitation.

1. A container, comprising: a container body defining a top opening, asealing surface being defined on the container body encircling the topopening; and a closure sealed to the sealing surface by a heat-sealmaterial comprising a blend of first and second acidic ionomers havingrespectively higher and lower acid content such that the heat-sealmaterial has an acid content intermediate between that of the first andsecond ionomers.
 2. The container of claim 1, further comprising aring-shaped end member attached to the container body encircling the topopening, the sealing surface being defined by the end member.
 3. Thecontainer of claim 2, wherein the end member comprises metal.
 4. Thecontainer of claim 1, wherein the first ionomer has an acid content ofabout 15% by weight and the heat-seal material has an acid content ofabout 11% by weight.
 5. The container of claim 1, wherein the firstionomer comprises a copolymer of ethylene and methacrylic acid whereinmethacrylic acid groups are partially neutralized with a cation.
 6. Thecontainer of claim 1, wherein the second ionomer comprises a copolymerof ethylene and acrylic acid wherein acrylic acid groups are partiallyneutralized with a cation.
 7. The container of claim 1, wherein thefirst ionomer comprises a copolymer of ethylene and methacrylic acidwherein methacrylic acid groups are partially neutralized with a cationand the second ionomer comprises a copolymer of ethylene and acrylicacid wherein acrylic acid groups are partially neutralized with acation.
 8. The container of claim 7, wherein the first and secondionomers are present in approximately equal proportions by weight in theheat-seal material.
 9. A container, comprising: a container bodydefining a top opening, a sealing surface being defined on the containerbody encircling the top opening; and a closure sealed to the sealingsurface by a heat-seal material comprising an acidic ionomer having anacid content of about 11% by weight.
 10. A container, comprising: acontainer body defining a top opening; a metal end attached to thecontainer body encircling the top opening; and a membrane closure sealedto the metal end by a heat-seal material comprising a blend of first andsecond acidic ionomers having respectively higher and lower acid contentsuch that the heat-seal material has an acid content intermediatebetween that of the first and second ionomers.
 11. A closure assemblyfor a container, comprising: a ring-shaped end member having a curlportion configured to be attached to a flange of a container bydouble-seaming, the end member further comprising a portion locatedradially inwardly from the curl portion and defining a sealing surface;and a flexible membrane closure configured to attach to the ring-shapedend member; wherein each of the end member and the closure has aheat-seal material disposed thereon for attaching the closure to the endmember by heat-sealing, the heat-seal material comprising a blend offirst and second acidic ionomers having respectively higher and loweracid content such that the heat-seal material has an acid contentintermediate between that of the first and second ionomers.
 12. Theclosure assembly of claim 11, wherein the first ionomer has an acidcontent of about 15% by weight and the heat-seal material has an acidcontent of about 11% by weight.
 13. The closure assembly of claim 11,wherein the first ionomer comprises a copolymer of ethylene andmethacrylic acid wherein methacrylic acid groups are partiallyneutralized with a cation.
 14. The closure assembly of claim 11, whereinthe second ionomer comprises a copolymer of ethylene and acrylic acidwherein acrylic acid groups are partially neutralized with a cation. 15.The closure assembly of claim 11, wherein the first ionomer comprises acopolymer of ethylene and methacrylic acid wherein methacrylic acidgroups are partially neutralized with a cation and the second ionomercomprises a copolymer of ethylene and acrylic acid wherein acrylic acidgroups are partially neutralized with a cation.
 16. A member for aclosure assembly of a container, comprising: a ring-shaped end memberhaving a curl portion configured to be attached to a flange of acontainer by double-seaming, the end member further comprising a portionlocated radially inwardly from the curl portion and defining a sealingsurface, and a heat-seal material disposed on the sealing surface forattaching a membrane closure to the end member by heat-sealing, theheat-seal material comprising a blend of first and second acidicionomers having respectively higher and lower acid content such that theheat-seal material has an acid content intermediate between that of thefirst and second ionomers.
 17. The member of claim 16, wherein the firstionomer has an acid content of about 15% by weight and the heat-sealmaterial has an acid content of about 11% by weight.
 18. The member ofclaim 16, wherein the first ionomer comprises a copolymer of ethyleneand methacrylic acid wherein methacrylic acid groups are partiallyneutralized with a cation.
 19. The member of claim 16, wherein thesecond ionomer comprises a copolymer of ethylene and acrylic acidwherein acrylic acid groups are partially neutralized with a cation. 20.The member of claim 16, wherein the first ionomer comprises a copolymerof ethylene and methacrylic acid wherein methacrylic acid groups arepartially neutralized with a cation and the second ionomer comprises acopolymer of ethylene and acrylic acid wherein acrylic acid groups arepartially neutralized with a cation.
 21. A flexible membrane closure fora container, comprising: at least one structural layer of flexiblematerial; and a heat-seal material joined to the at least one structurallayer and exposed at one surface of the closure for heat-sealing to asealing surface provided on a container, the heat-seal materialcomprising a blend of first and second acidic ionomers havingrespectively higher and lower acid content such that the heat-sealmaterial has an acid content intermediate between that of the first andsecond ionomers.
 22. The flexible membrane closure of claim 21, whereinthe first ionomer has an acid content of about 15% by weight and theheat-seal material has an acid content of about 11% by weight.
 23. Theflexible membrane closure of claim 21, wherein the first ionomercomprises a copolymer of ethylene and methacrylic acid whereinmethacrylic acid groups are partially neutralized with a cation.
 24. Theflexible membrane closure of claim 21, wherein the second ionomercomprises a copolymer of ethylene and acrylic acid wherein acrylic acidgroups are partially neutralized with a cation.
 25. The flexiblemembrane closure of claim 21, wherein the first ionomer comprises acopolymer of ethylene and methacrylic acid wherein methacrylic acidgroups are partially neutralized with a cation and the second ionomercomprises a copolymer of ethylene and acrylic acid wherein acrylic acidgroups are partially neutralized with a cation.